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From "Daniel John Debrunner (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Wed, 19 Mar 2008 16:34:24 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12580439#action_12580439
] 

Daniel John Debrunner commented on DERBY-481:
---------------------------------------------

In the spec:
> We rename the sqlAllowed field of RoutineAliasInfo and borrow one of its bits to encode
whether a routine is DETERMINISTIC.

RoutineAliasInfo already has a field set up for expansion, I think we can use this in a smart
way instead of making a single field handle multiple meanings (less clear). I've always been
planning to add all the possible future options for routines into RoutineAliasInfo, I'd be
willing to handle that portion for this improvement.

> implement SQL generated columns
> -------------------------------
>
>                 Key: DERBY-481
>                 URL: https://issues.apache.org/jira/browse/DERBY-481
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>    Affects Versions: 10.0.2.1
>            Reporter: Rick Hillegas
>         Attachments: GeneratedColumns.html
>
>
> Satheesh has pointed out that generated columns, a SQL 2003 feature, would satisfy the
performance requirements of Expression Indexes (bug 455). Generated columns may not be as
elegant as Expression Indexes, but they are easier to implement. We would allow the following
new kind of column definition in CREATE TABLE and ALTER TABLE statements:
>     columnName GENERATED ALWAYS AS ( expression )
> If expression were an indexableExpression (as defined in bug 455), then we could create
indexes on it. There is no work for the optimizer to do here. The Language merely has to compute
the generated column at INSERT/UPDATE time.

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